The formation of various integrated circuit (IC) structures on a wafer often relies on lithography processes, sometimes referred to as photolithography. For instance, patterns can be formed from a photoresist layer by passing light energy through a mask (or reticle) having an arrangement to image the desired pattern onto the photoresist layer. As a result, the pattern is transferred to the photoresist layer. In areas where the photoresist is sufficiently exposed and after a development cycle, portions of the photoresist material can become soluble such that it can be removed to selectively expose an underlying layer (e.g., a semiconductor layer, a metal or metal containing layer, a dielectric layer, etc.). Portions of the photoresist layer not exposed to a threshold amount of light energy will not be removed and serve to protect the underlying layer. The exposed portions of the underlying layer can then be etched (e.g., by using a chemical wet etch or a dry reactive ion etch (RIE)) such that the pattern formed from the photoresist layer is transferred to the underlying layer. Alternatively, the photoresist layer can be used to block dopant implantation into the protected portions of the underlying layer or to retard reaction of the protected portions of the underlying layer. Thereafter, the remaining portions of the photoresist layer can be stripped.
There is a pervasive trend in the art of IC fabrication to increase the density with which various structures are arranged. As a result, there is a corresponding need to increase the resolution capability of lithography systems. One promising alternative to conventional optical lithography is a next-generation lithography technique known as immersion lithography. In immersion lithography, an immersion lithography medium is placed between the final lens of the imaging system and a photosensitive material (e.g., a photoresist) on the surface of a nascent semiconductor device. The desired pattern of radiation is transmitted through the immersion lithography medium to the photosensitive material. The immersion lithography medium replaces an air (or other gas) gap that is conventionally present between the final lens of a conventional dry lithography imaging system and the wafer. When the immersion lithography medium has an index of refraction higher than 1 (the index of refraction of air), the numerical aperture of the imaging system can be effectively increased, thereby enhancing resolution of the lithography process.
However, attempts to implement immersion lithography have encountered a number of challenges. Accordingly, there exists a need in the art for improved immersion lithography processes.